Photo-electric apparatus



June 15 1926.

R. HART PHOTO-ELECTRIC APPARATUS v Filed August 22, 1925 U. 0 U U U\ U D U U Inventor;

ussez Hart, WM Attorney Patented l rine ll& THE&

BUSSELL HART, Olt LUS lmao ANGELES, CALIFORNA 'EHOTO-ELECTRU APPAEATUS.

Application filed August 22, 1925. Serial No. 51,850.

In this specification, and the accompanying drawing, T shall describe and show a preferred form of my invention, and specifically mention certain of its more important objects. li do not limit myself to the forms disclosed, since various changes, and adaptations may be made therein with out departing from the essence of my invention as hereinafter claimed; and -objects and advantages, other than those specifically mentioned, are included within its scope.

My invention relates to means for photographically recording variations in a modulated electric current, and it is applicable to such uses as the photographic recording of sound waves and 'for tele-photographic receiving. Its principal objects include: first, to provide an apparatus that is specially adapted for this general purpose and which is exceedingly sensitive, and responsive to the most minute variations in an electric current; second, to supply facilities for recording electric modulations in either of two distinct ways viz, by means of a record of sub- M stantially uniform width and varying density, and by means of a record of Varying width and substantially uniform density; third, to make it possible to produce a very sharply defined 'record of either of the above types upon a photographic film, while running at the standard speed employed in the motion picture art; and, fourth, to accomplish all of the foregoing objects in a single apparatus of relatively great Simplicity and small cost.

My objects are attained by means of the apparatus illustrated in the accompanying drawing, in which- V Figure 1 is a plan View of the entire recording portion of my apparatus;

Figure 2 is an enlarged elevation, shown partly in section, of an approved lightmodulating means;

Figure 3 is an enlarged elevation of the cylindrical mirror I employ in connection with my apparatus, and the means whereby it may be adjusted to allow of producing either of the types of record described above;

Figure 4 is an elevation of the type of primary light source I prefer to employ;

Figure 5 is a plan View of a fragment of motion picture film with a sound record there'on of the varying density type; and

Figure 6 is a plan view of a similarfilm with a sound record of uniform density and variable width.

Similar reference numerals refer to similar parts throughout the several views.

Tn previous applications tor United States patents T have illustrated and described means for producing similar sound records, and for reproducing sound therefrom. have not hitherto shown or described, however, the specific means illustrated and claimed herein. 4

Before passing to a detailed description of my present inrention it is to be noted that the standard speed of motion picture film is about one foot per second; and that the frequency of the modulations it may be desired to record is often as high as 5000 cycles per second. Consequently the successive peaks of the record may be only about two thousandths of an inch apart. Such a record must 'be exceedingly sharp and clearly defined to allow ot' reproduction without blurring or distortion. Any such efl'ect as overlapping of successive peaks is fatal to satisfa'ctory reproduction.

In the embodiment of my invention selected 'for illustrative purposes, T employ for the primary light source a tubular lamp 7, having a reasonably rugged rectilinear filament 8 therein. This filament is mounted under tension between resilient terminals 9, in such manner that the filament will remain under tension when heated, and thus be able to maintain its rectilinearity.

The rays 10 from the incandescent filament are permitted to fall upon a small cylindrical mirror 11, and to be reflected thereby through a focusing lens system 12, upon a photographic film 13. The efi ect of attenuation of an image produced by a cylindrical mirror is well known, and this effect varies inversely to the radius of the mirror. If,

therefore, the filament 8 is say 1/100 of an inch in diameter, the reflected image of the filament may easily be made 1/1000 of an inch in width by employing a sufliciently small radius for the mirror. A secondary image of the above primary image is focused upon film 13 by lens system 12, and .the secondary image can easily be made still more tenuous by means of the lens. In this manner it is possible to throw an exceedingly narrow band of light upon the film for exposure purposes.

While being exposed, the film 13 is 'moved at a unifo-rm speed by means of sprocket llG drum 14, and it 'is held in contact with the r drumby means of its tension and the assistance of guide rollers 15. The film is housed within a light-tight box of which a portion of the wall is indicated in section at 16.

For modulating the film exposure I may use various types of electro-magnetic devices for variably intercepting the light rays from the filament before they fall upon the mirror. A preferred type of apparatus for ths purpose is indicated at 17, and its Construction and functioning will be best understood by considering Figures 1 and 2, and especially the latter.

This illustrated ray interceptor comprses an electro-magnet having an exciting coil 18, a circularly bored pole 19, and a cylindrial pole 20 within the bored pole. This devce is mounted upon a base 21 of non-magnetc material. Within the tubular gap between the two poles is the modulating coil 22 wound upon a floating tubular shell 23. This shell is mounted upon a light fourarmed spider 24 which, in turn, is supported by a thin strip 25 of resilient material attached to the outer face of pole 19. The

spider is attached to the strip by means of a screw 26, and the latter carries a knifeedged target 27 at its outer end. Coil 22 is connected by its leads 28 in the circuit whose modulations it is desired to record, and the variations in the current will cause target 27 to vibrate in its own plane in consonance therewith. I usually find it desirable to mount the strip 25 between washers of-fibrous material such as paper, as shown at 29; and usually also- I employ pieces of sponge rubber 30, crowded between this strip and the fingers 31, to damp the vibrations of the strip. I have found that sheet aluminum is a satisfactory material of which to make strip 25.

The interceptor is set upon base 21 with knife edge 32 of its target in the path of rays 10, and as close as possible to mirror 11, the plane of the target being perpendicular to the rays. The vibrations of the target will thus cause the rays to be variably intercepted, and thereby vary the exposure of film 13.

It is important that target 27 should' be positioned as described since the greatest result is obtained in this manner. When so positioned a vibration of even minute amplitude will produce a noticeable variation in the exposure of the film. This, makes it possible to record the slightest variations in the modulated current in true and undistorted relation as to both frequency and amplitude.

For producng the ,type of record illustrated at 33, the axis-'of mirror 11 is made p'arallel to knife-edge 32. Vibration of the target in this case causes a corresponding variation in the' width of the prim'ary image reflected from the mirror, the length of the image remaining constant. The resulting eximage produces a record of uniform density with a sharply serrated edge.

The adjustment of the mirror is efi'ected by angularly and longitudinally positioning its supporting bar 35, and is maintained by set screw 36. i

In all apparatus designed to acconplish the purposes of this invention, the 'greatest difliculties have been: to secure the requiste degree of fineness of the record; to prevent overlapping of the succeeding modulations; and to obtain freedom from the effects of such outside influences as vibration, temperature changes, and distorti'on due to electromagnetic and electro-static fields. The apparatus described is capable of overcoming all these difliculties in a high degree, and by its use I have succeeded repeatedly in producing eninently satisfactory sound records;

Such records when properly used have iven the most faithful of reproductions an are particularly notable for intonation, clear articulation, and quality of tone.

The preceding description has suggested the use of this invention for recording sound for reproduction. For this purpose a current is telephonically modulated and made to pass through coil 22. Obviously records can be made n a similar manner when the current in coil 22 is photo-modulated. The invention is thus adapted for the purposes of telephotography. For the latter purpose supplementary means must be provided for imparting a lateral movement to the film to accomplish scannin Various means have already een developed and are known tothose familiar with the art concerned. Such means 'do not co'nstitute a part of the present invention and are not claimed herein.

I claim 1. Apparatus 'of the character described, comprising; a rectilinear light source; a uniformly movable photo-sensitized surface; a cylindrical mirror whereby an image of said source may be reflected upon said surface; and means -for variably eclipsing rays from said source to modify the proportions of the refiected image to correspond to modulations of current in an electric circuit.

2. Apparatus of the character described, comprisng; a rectilinear light source; a uniformly movable photo-sensitized surface; a cylindrical mirror whereby an attenuated scanning r filament may mes me image of said source may be reflected upon said surface transversely to its direction of motion; and means for variably eclipsing rays from said source to modify the area of the reflected image to correspond to modu1ations of current in an elcctric circuit 3. Apparatus of the character described, comprising; an iiluminable rectilin-ear filament; a uniformiy movabie photo-sensitized surface; a cylindrical mirror whereby an attenuated image of said filament may be reflected upon said surface transverseiy to its direction 'of motion; and a target vibratiie to moduiations of current in an electric circuit, whereby radiations from said fiiainent may be -variably eclipsed between the filament and mirror to modify the prcportions of said reflected image.

4. Apparatus of the character described, comprising; an iiluminable rectilinear filament; a uniformly movable photo-scnsitizcd surface; a cylindrical mirror of small radius, whereby a much attenuated image of said be refiectcd upon said surface transversely to its direction of motion; and a sharp-edged target adj acent the mirror and vibratile to nodulations of current in an electric circuit, whereby radiations from said filament may be variably eciips'ed between the filament and mirror to modify the area of said reflected image.

5. Apparatus of the character described, comprisingj an iliuminable rectiiinear fiia ment; a uniformly movable photo-sensitized surface; a cylindrical mirror of small ra-dius, whereby a much ,attenuated image of said fiiament may be reflected upon said surface transverseiy to its direction of motion; and a sharp-edged target adjacent the mirror and vibratile in its own plane to moduiations of current in an electric circuit, whereby radiations from said fiiament may be variabiy eclipsed between the filament and mirror, to modify the area of said refiected image in proportion to said m-odulations.

6. Apparatus of the character described, comprising; an illuminable rectilinear filament; a uniformly movable photo-sensitized surface; a cylindrical mirror of small radius, whereby a much attenuated image of said filam'ent may be reflected upon said surface transversely to its direction of motion; a iens intermediate said mirror and said surface; and a target adjacent the mirror and vibratile in its own plane to modulations of current in an electric circuit; said target be ing intermediate said filament and said mirror, and having a sharp edge whereby radiations from the filament may be Variabiy eclipsed to modify the area 'of said reflected image in proporton to said modulations.

RUSSELL HART. 

